<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>13边框</title>
    <style>
        body{
            background-color: black;
        }
        .c1 {
            height: 300px;
            width: 500px;
            border-left: 20px solid transparent; /*solid实线 dotted虚线 double双层*/
            border-right: 20px double transparent;

            border-top: 20px solid red;
            border-bottom: 20px solid transparent;

            margin: 100px;
        }
        .c1:hover{
            border:20px dotted  white;
        }

    </style>
</head>
<body>
<div class="c1">
    <p style="color: white">框在这</p>
</div>

</body>
</html>